1. Field of the Invention
This invention relates to a method for the production of a dielectric-separation substrate possessed of a supporting member made of polycrystalline siliicon and intended for use in a semiconductor integrated circuit.
2. Description of the Prior Art
Generally, in the semiconductor integrated circuit, since circuit elements such as transistors, diodes, and resistors are integrally formed in a part of a single crystal substrate, these integrated circuit elements must be electrically insulated and separated. As means for the mutual separation of the elements, the pn junction separation, the dielectric separation, etc. are available. The dielectric separation has the advantage of a high voltage breakdown and a small parasitic capacitance as compared with the pn junction separation and, therefore, permits production of a semiconductor integrated circuit of a high voltage breakdown, a large capacity, and a high operating speed. The utilization of this method, therefore, has been drawing attention.
The conventional method for the production of a dielectric-separation substrate, as illustrated in FIG. 2a to FIG. 2c, comprises incising grooves 15 in a single crystal silicon substrate 14, then depositing a polycrystalline silicon on the surface of the single crystal silicon substrate 14 including the grooves 15 thereby forming a polycrystalline silicon layer 17, further grinding the surface of the polycrystalline silicon layer 17, and subsequently grinding the rear surface of the single crystal silicon substrate 14 till the bottom parts of the grooves 15 thereby giving rise to separated single crystal silicon islands 18 and completing a dielectric-separation substrate 19.
In the method described above, when the polycrystalline silicon is deposited at an elevated temperature on the single crystal silicon substrate 13, a warpage exceeding 100 .mu.m occurs in a 4 inch wafer. The substrate sustaining this warpage fails to adhere fast through the medium such as of Wax to a glass plate during the grinding of the surface of the polycrystalline silicon layer 17 or the surface of the single crystal silicon substate 14. If the grinding is carried out in spite of the warped substrate, the single crystal silicon islands 18 have uneven thicknessess as illustrated in FIG. 4 and, at times, these single crystal silicon islands 18 may be incompletely separated. When dielectric-separation substrates of such a defective quality are used, semiconductor integrated circuits cannot be manufactured in a satisfactorily high yield. For the solution of this problem, Japanese Patent Publication SHO 56(1981)-35,024 discloses a method which comprises alternately superposing polycrystalline silicon layers and oxide films. Since the step for deposition of polycrystalline silicon is complicated, this method suffers from high cost and poor productivity.